Electrical charging systems are increasing in complexity, power delivery, and other features, such as wireless charging. Remote systems, such as vehicles, include locomotion power derived from electricity received from an energy storage device, such as a battery. For example, hybrid electric vehicles include on-board chargers that use power from vehicle braking, traditional motors, and other innovations to charge power storage units in vehicles. Vehicles that are solely electric generally receive electricity for charging its batteries from additional sources, for example a wired alternating current (AC) such as household or commercial AC supply through a power outlet connected to a power grid. The wired charging connections cables are physically connected to a power supply. Wireless power charging systems that are capable of transferring power in free space (e.g., via a wireless field) overcome some of the deficiencies of wired charging solutions to charge electric vehicles. As such, wireless power charging systems and methods that efficiently and safely transfer power for charging electric vehicles are desirable.
Inductive power transfer (IPT) systems are one means for the wireless transfer of energy. In IPT, a primary (or “base”) power device (e.g., a base pad, wireless power transfer pad, a wireless power transfer element, base wireless charging system, or some other wireless power transfer device including a power transfer element (e.g., base power transfer element)) transmits power to a secondary (or “pick-up”) power receiver device (e.g., a vehicle pad, an electric vehicle wireless charging unit, or some other wireless power receiving device including a power transfer element (e.g., vehicle power transfer element)). Each of the transmitter and receiver power devices includes inductors, typically coils or windings of electric current conveying media. An alternating current in the primary inductor produces a fluctuating magnetic field. When the secondary inductor is placed in proximity to the primary inductor, the fluctuating magnetic field induces an electromotive force (EMF) in the secondary inductor, thereby transferring power to the secondary power receiver device.
For example, in wireless electric vehicle charging (WEVC) systems, the alternating current in the primary inductor is commonly supplied by a pulse width modulated (PWM) inverter connected to a power source to supply a square wave voltage through a cable (or “feed line”) to a base power transfer element. The base power transfer element includes resonant tank circuitry (e.g., circuitry comprising a combination of a capacitance component (C) and an inductance component (L)) configured to operate a resonant frequency using any number of compensation strategies. For example, compensation strategies such as LC, LCL, SS, SP, PS, and PP are widely adopted, where the first S (series) or P (parallel) represents a capacitor in series or parallel, respectively, with a transmitter coil and the second S or P stands for capacitor in series or parallel, respectively, with the receiver coil. It will be appreciated that other compensation strategies are within the scope of the disclosure. Accordingly, in some embodiments, the square wave is generated at the resonant frequency of the resonant tank circuitry.
The square wave voltage supplied to the base power transfer element may lead to unwanted frequencies (e.g., harmonic frequencies) being generated in the WEVC system including at the base power transfer element and at a vehicle power transfer element wirelessly coupled to the base power transfer element, as well as at other components coupled thereto. Such unwanted harmonics may lead to undesired non-sinusoidal currents and voltages in components of the WEVC. For example, even though an LCL compensation strategy generally serves to deliver uninterrupted power and smoother power transitions, the resonant tank circuitry and/or other components of a wireless power transfer device including the base power transfer element may reflect reactive power back towards the power source through the feed line causing efficiency losses and heat. Accordingly, these unwanted harmonics reduce system efficiency (e.g., due to hysteresis and eddy current losses). Further, the heat generated can degrade the base power transfer element including system capacitors and other components resulting in long-term reliability issues, EMI safety concerns, and poor performance.
Designers of IPT systems are often under continual pressure to make smaller, lighter, and generally more compact IPT systems and/or to adapt IPT systems to certain design criteria (e.g., parking lot dimensions for a WEVC system). Adding additional circuitry to the base power transfer element or the power supply to reduce unwanted frequencies in an IPT system may add size and complexity where space is at a premium. Thus there is a need in the art for improvements to IPT frequency filtering.